(Sunday, 7/14/2019) 4:00 PM - 5:00 PM
Room: 302
Purpose: Radiation induced interstitial pneumonitis and late renal dysfunction are major concerns for patients undergoing total body irradiation (TBI). The purpose of this work is to evaluate the dosimetry of VMAT-based TBI plans generated using Varian Eclipse scripting.
Methods: Three full-body CT datasets (two patients, one anthropomorphic CIRS phantom) were used. An in-house Eclipse script was developed to generate optimized field arrangements using the body contour, user origin, and couch longitudinal travel. Plans consisted of a lower-body AP/PA portion and an upper-body VMAT portion (8 full arcs with 4-isocenters). Treatment plans to 1320cGy (165cGy x 8fx) were generated with dose directives: [PTV V100%≥90-95%; Total lung Dmean<900cGy; Kidneys Dmean<1100cGy]. All plans used 6MV photons and were calculated using the AAA algorithm. Upper-body VMAT plan dosimetry was evaluated ‘in-phantom’ placing 12 OSLDs in different key locations (lung, kidneys, bone, and soft tissue). Additionally, dosimetric verification was performed for the three plans using Varian portal dosimetry, PerFraction(SNC) and ArcCheck(SNC) with a global gamma criterion of 2%/2mm.
Results: Planning objectives were met for the three treatment plans with the following averages: PTV V100%=94.02%, total lung Dmean=872.9cGy, and kidneys Dmean=1075.8cGy. The dose deviation between Eclipse and the OSLDs (relative to the prescribed dose) averaged 0.98%, with each individual dose deviation within ±4%. Dose ranged between 52.5cGy (lung) and 187.5cGy (bone) for OSLD measurements. The average passing rate for all 24 fields (8 per plan) was 98.0%, 99.76% and 98.6% for portal dosimetry, PerFraction and ArcCheck respectively. The lowest passing rate of any individual field was 95.4%, 99.0% and 91.8% for portal dosimetry, PerFraction and ArcCheck respectively.
Conclusion: Eclipse scripting can assist in creating robust multi-isocentric VMAT-based TBI treatment plans to block lungs and kidneys without compromising target coverage. Dosimetric accuracy and deliverability was confirmed using in-phantom OSLD dosimetry, Varian portal dosimetry, PerFraction and ArcCheck verification.
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